Molecular characterization of infectious laryngotracheitis virus in China and host transcriptomic responses to immunization with a live attenuated vaccine

Infectious laryngotracheitis (ILT) is a respiratory disorder that poses a global threat to poultry production. It is caused by infectious laryngotracheitis virus (ILTV), a member of the family Orthoherpesviridae. The pathogenicity of different strains of ILTV in intensive poultry operations varies among regions, and the local prevalence of individual strains affects their prioritization in biosafety strategies. Vaccination is the primary method used for controlling ILT. In this study, we sequenced selected genes of ILTV isolates from Zhejiang, China, and analyzed the transcriptome to evaluate the response to immunization of chickens with an attenuated inactivated vaccine. We identified two specific strains of ILTV and compared the sequences of their immune- and virulence-related genes. The results indicated that multiple specific amino acid mutations were located in glycoprotein B, glycoprotein D, and thymidine kinase. The transcriptome of the spleens of chickens that were immunized with a live attenuated vaccine was analyzed, and the immunized group was found to have 33 upregulated and 79 downregulated genes compared with the control group. The differentially expressed genes related to immunity were mainly enriched in the intestinal immune network. The findings of this study provide insights into the genetic diversity of ILTV in Zhejiang and also suggest target genes and pathways that are affected by immunization, providing new information that will facilitate further research on preventing and controlling avian diseases and contribute to our understanding of the molecular mechanisms underlying the immune responses of poultry.